best practice for advertising peering fabric routes

William Herrin bill at
Wed Jan 15 18:26:57 UTC 2014

On Wed, Jan 15, 2014 at 12:54 PM, Niels Bakker <niels=nanog at> wrote:
> * nanog at (Jim Shankland) [Wed 15 Jan 2014, 18:04 CET]:
>> So ... RFC1918 addresses for the IXP fabric, then?
>> (Half kidding, but still ....)
> They need to be globally unique.

Hi Niels,

Actually, they don't. To meet the basic definition of working, they
just have to be able to originate ICMP destination unreachable packets
with a reasonable expectation that the recipient will receive those
packets. Global uniqueness is not required for that. However, RFC1918
addresses don't meet the requirement for a different reason: they're
routinely dropped at AS borders, thus don't have an expectation of
reaching the external destination.

Of course working, monitorable and testable are three different
things. If my NMS can't reach the IXP's addresses, my view of the IXP
is impaired. And "the Internet is broken" is not a trouble report that
leads to a successful outcome with customer support... it helps to be
able to pin things down with some specificity.

Bill Herrin

William D. Herrin ................ herrin at  bill at
3005 Crane Dr. ...................... Web: <>
Falls Church, VA 22042-3004

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